Disrupting effects of azocyclotin to the hypothalamo-pituitary-gonadal axis and reproduction of Xenopus laevis

Over the past few decades, the hazards associated with the extensive use of organictin compounds have become an issue of extreme concern, while at present the effects of these substances on amphibians remain poorly understood. In the present study, we chose azocyclotin, one of common use acaricides in China. We focused on sexual development and steroidogenesis disrupting effects of azocyclotin in the Xenopus laevis. Tadpoles were exposed to azocyclotin (0.05 and 0.5 μg/L) for long-term (4 months) study. Results showed that exposure to azocyclotin caused developmental toxicity, including decreased survival, body weight, body length, gonadosomatic index, hepatosomatic index and female phenotype. At the same time, statistical increase in mean age at completion of metamorphosis was observed in azocyclotin treatments in comparison with control group. Furthermore, hormone concentrations, and steroidogenesis genes expression of adult frog were further evaluated in 28 days exposure. Results demonstrated that the key regulating hormones, e.g. testosterone and pregnenolone, were significantly upregulated. The expression levels of selected steroidogenic genes were also significantly altered. Our study demonstrated that azocyclotin could delay the metamorphosis and disrupt the gonadal differentiation of X. laevis. Steroidogenesis and the expression of genes involved in the hypothalamus-pituitary-gonadal-liver axis in frogs were disrupted after azocyclotin exposure. Azocyclotin showed both androgenic and antiestrogenic activity for X. laevis. Those findings emphasized the influence of azocyclotin on non-target species in the context of ecotoxicological risk assessment.